the Book of Jasher and Jubilees do not contradict each other (at least, not in their original documents). Enoch has been canonized, and that contradicts Rabbinic and Pharisee calendar. Oh, but you'll say, Enoch isn't reliable in that one place concerning the calendar, but about everything else it is scripture. Why couldn't the same be said when Jasher contradicts Jubilees? How can we put so much trust in the Book of Jasher moreso that Jubilees? We have copies of Jubilees that date back to 200 BC. For the Book of Jasher, we have no surviving manuscripts to verify that it even existed before 1625 AD. While I accept both as canonical, doesn't it seem a bit silly to suggest that Jasher is more reliable than Jubilees? The earliest copy of Jubilees precedes the earliest copy we have of Jasher by about 1800 years. I think that is pretty significant, don't you?
The incident James Trimm cited however I don't think contradict each other, and I use Jasher to interpret what Jubilees meant in the case of Cain's death.
If you can agree that Yahushua ate on the Passover or the Feast of Unleavened Bread, you will see that there are indeed two calendars.
why the (pesach) feast dates coming variation?
--because the christians put the easter sunday as the dominant day, so that easter should fall on the nearest sunday and count three days backwards for the good friday and so on.
--while the Jews and few oriental churches follow the counting of the new moon and from it counts for Pesach.
--a closer study of the "quartodeciman" quarrel of the early church history may help understand why the variance between the east and west. those who follow Yohann the apostle kept the pesach according to the Jewish calendar; while those who follow rome (west) held separate dates. the church almost had an earlier schism on this account had the matter not been properly handled by the two big leaders. this is another historical evidence indicating that the apostles remained shomeyr mitzvoth even in their preaching days.